#!/usr/bin/python

import email, difflib, re, sys

inmail="""From: <foo@bar.baz>
To: <baz@bar.foo>
Subject: test
X-Long-Line: Some really long line contains a lot of text and thus has to be rewrapped because it is some
	really long
        line
MIME-Version: 1.0
Content-Type: multipart/signed; boundary="borderline";
	protocol="application/pgp-signature"; micalg=pgp-sha1

This is an OpenPGP/MIME signed message (RFC 2440 and 3156)
--borderline
Content-Type: text/plain
X-Long-Line: Another really long line contains a lot of text and thus has to be rewrapped because it is another
	really long
        line

This is the signed contents.

--borderline
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: OpenPGP digital signature
Content-Disposition: attachment; filename="signature.asc"

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.0.6 (GNU/Linux)

iD8DBQFG03voRhp6o4m9dFsRApSZAKCCAN3IkJlVRg6NvAiMHlvvIuMGPQCeLZtj
FGwfnRHFBFO/S4/DKysm0lI=
=t7+s
-----END PGP SIGNATURE-----

--borderline--
"""

# This is a semantic no-op: parse mail and turn it back into a string.
outmail = email.message_from_string(inmail).as_string(False)

# Extract the first mime part of each message
repart = re.compile(r'^--([^\n]+)\n(.*?)\n--\1$', re.DOTALL | re.MULTILINE)
inpart = repart.search(inmail).group(2)
outpart = repart.search(outmail).group(2)

if inpart == outpart:
    print 'All is well: the signed part survived without any modifications.'
    sys.exit(0)
else:
    print 'Bad news: the signed part was modified, which broke the signature.'
    print '\n'.join(difflib.unified_diff(inpart.split('\n'),
                                         outpart.split('\n'),
                                         fromfile='in.eml',
                                         tofile='out.eml',
                                         lineterm=''))
    sys.exit(1)